How to convert a TxnExpr to Int

I try to convert a pyteal.TxnExpr to Int with :
But I get error :

pyteal.TealInputError: invalid input type <class ‘pyteal.TxnExpr’> to Int

I need to do that in order to use this int value to check another transaction.
How should we do the conversion to Int ?

you don’t need to convert it to Int() explicitly.
you can directly compare the values directly.

Assert(txna.asset_amount() == txnb.asset_amount())